Is there a way to subdivide a face without using ctrl r and creating unnecessary polygons?
Yes you can, by creating "n-gons". Bad for topology, usually but it can be done like this:

in edit mode select just the side edges of the slope then subdivide them enough (use edge tools > subdivide - CTRLE): 



you get edges subdivided as you want along their length. Now activate vertex snapping, and in side mode select vertices like this



then (with all those vertices selected) grab them along global Z and snap to their bottom unselected vertices



then do the same but on global Y with their upper unselected vertices



you get this in the end:



of course this is just a simple example...